update gradle to version 7.6 (#2744)

* update gradle to version 7.6

* update hash
diff --git a/build/docker/old/ubuntu-xenial/Dockerfile b/build/docker/old/ubuntu-xenial/Dockerfile
index add524d..63140ac 100644
--- a/build/docker/old/ubuntu-xenial/Dockerfile
+++ b/build/docker/old/ubuntu-xenial/Dockerfile
@@ -155,7 +155,7 @@
       haxelib install --always hxcpp 3.4.64 2>&1 > /dev/null
 # note: hxcpp 3.4.185 (latest) no longer ships static libraries, and caused a build failure
 
-ENV GRADLE_VERSION="7.5.1"
+ENV GRADLE_VERSION="7.6"
 RUN apt-get install -y --no-install-recommends \
       `# Java dependencies` \
       ant \
@@ -165,7 +165,7 @@
       unzip && \
       `# Gradle` \
       wget https://services.gradle.org/distributions/gradle-$GRADLE_VERSION-bin.zip -q -O /tmp/gradle-$GRADLE_VERSION-bin.zip && \
-      (echo "f6b8596b10cce501591e92f229816aa4046424f3b24d771751b06779d58c8ec4  /tmp/gradle-$GRADLE_VERSION-bin.zip" | sha256sum -c -) && \
+      (echo "7ba68c54029790ab444b39d7e293d3236b2632631fb5f2e012bb28b4ff669e4b  /tmp/gradle-$GRADLE_VERSION-bin.zip" | sha256sum -c -) && \
       unzip -d /tmp /tmp/gradle-$GRADLE_VERSION-bin.zip && \
       mv /tmp/gradle-$GRADLE_VERSION /usr/local/gradle && \
       ln -s /usr/local/gradle/bin/gradle /usr/local/bin